Energy storage systems (e.g., battery energy storage systems) have become increasingly used to deliver power either as part of standalone energy storage systems or as part of power generation systems (e.g., a wind farm, solar farm, gas turbine system) with an integrated energy storage system. Energy storage systems are unique in that energy storage systems have the ability to both deliver and reserve energy for particular services. Energy storage systems can include one or more battery banks that can be coupled to the grid or other load via a suitable power converter.
FIG. 1 depicts a schematic of a power converter topology 50 that can be used to interface a low voltage bus 60 with a high voltage bus 70. As shown, the low voltage bus can be coupled to a node between switching element S1 and switching element S2 through inductor L1. The switching elements S1 and S2 can be power switching devices, such as insulated gate bipolar transistors (IGBTs), power MOSFETs, or other suitable switching devices. The switching elements S1 and S2 can be controlled to transfer power between the low voltage bus 60 and the high voltage bus 70. Low voltage bus 60 is referenced to ground through capacitor C1. High voltage bus 70 is referenced to ground through capacitor C2. Both the low voltage bus 60 and the high voltage bus 70 are ground-referenced.
High voltage batteries used in energy storage systems are often operated in floating systems to facilitate insulation between the system components and ground. In some cases, it can be desirable to connect the energy storage system to a ground-referenced bus for sourcing or sinking power. For instance, in can be desirable to allow a grounded, high voltage photovoltaic array to be used to charge a floating battery system. The power converter topology 50 of FIG. 1 would be inappropriate for such applications as the power converter topology 50 is intended for bidirectional power transfer between two ground-referenced systems. Transformer-based power converters can be used to couple a floating system with a ground-referenced bus. This can provide for galvanic isolation but can also cause a reduction in efficiency.
Thus, a need exists for a power converter topology that allows power to be transferred bidirectionally between a floating system and a ground-referenced system.